Crystal diodes



J. W. DAWSON CRYSTAL DIODES June 23, 1959 Original Filed'June 29, 1954MN 55355 35m INVENTOR JOHN W. DAWSON ATTORNEY United States PatentOflice 2,892,136 Patented June 23,, 1959 CRYSTAL DIODES John W. Dawson,Winchester, Mass, assignor to Sylvania Electric Products, Inc., Salem,Mass, a corporation of Massachusetts Continuation of application SerialNo. 440,168, June 29, $954. O'Ihis application-December 19, 1955,-SerialNo. 53,90

7 Claims. (Cl; 324-158) The-present invention relates to testingandcomparing systems, and particularly to a method and apparatusforelectrically comparing groups of diodes, especially pointcontactcrystal rectifiers, with reference to a particular characteristic orproperty. This application is a continuation of my copendingapplication, Serial No. 440,168, filed June 29, 1954, now abandoned.

With the extensive application of germanium crystal diodes for videodetection and allied circuit designs, it has become exceptionallyimportant to measure the various properties or characteristics ofgermanium diodes, such as dynamic efiiciency as a video detector,current values at specified voltages, back and forward IEcharacteristics,

diode capacitance, and the like. For example, productionchecking ofstatic crystal characteristics may be accomplished by successivelyinserting diodes to be tested into a balanced amplifier bridge forcomparison with a standard diode, suitable rejection-acceptance limitsbeing set in accordance with the required production standards; Theresult of the individual comparison tests are listed on a chart and thediodes sortedinto matched pairs for balanced detectors or sets offourfor varistors. The tediousness and imperfection of this technique aremanifest, especially when processing a large number of diodes.-

Accordingly, it is an object of the present invention to provide a novelmethod and apparatus for measuring characteristics of electricaldevices, especially point-contact crystal rectifiers.- Moreparticularly, it is an object of this, invention to provide for theautomatic sequential comparing of plural electric devices with astandard for ascertaining when a given property of the sequentiallytested devices and the standardsubstantially coincide.

It is within the contemplation of this invention a system for taking alarge number ofelectrical devices, such as crystal rectifiers, and tosequentially compare each of the devices against every other device asto a particular electrical characteristic, and when sutficientidentityin the particular characteristic exists, to automatically recordcoincidence on a chart from which the devices can be sorted into groupsidentical with respect to the particular characteristic.

Many other objects, salutory advantages andfeatures will occur to thoseskilled in the art as the detailed description proceeds. In order torender the understanding of this invention complete and lucid, andfurther to comply with the statutes relatingto the same, and to pointout precisely where a patentable advance in the arts and sciences hasbeen made, there has been shown aspecific embodiment of the invention inthe accompanying drawing, wherein:

The single figure is a. diagrammatic showing of a preferred embodimentof the testing device for grouping diodes identical with respect to aselected characteristic.

Referring now specifically to the drawing, there is shown a hollowturret or carrier 10, arranged to extend generally vertically andsupported for intermittent indexing about a horizontal axis byanintegralsleeve 12, joura naled within a fixed bearing 14 of a support, notshown.

Arranged at' spaced peripheral locations about the turret or carrier 10,are cooperating pairs of support and contact fingers 16, 18, 16', 18',each of a springy conductive material. The respective pairs ofsupporting and contactfingers support the individual point-contactcrystal rectifiers, one being arbitrarily designated as a standard Sanda further one, being arbitrarily designated as a crystal under testT.

Arranged coaxially of and within the sleeve 12 of the turret 10 is ashaft 20, which is journaled adjacent its opposite ends by bearings22,24. The shaft 20 is con,- ductively insulated from the sleeve 12 ofthe turret 10" by provision of a non-conductive separator or spacer 26inter-- mediate the shaft 20 and the sleeve 12. Disposed within theturret 10 and fixed to the shaft 20 is a rotatable contact arm 28.including a pair of outwardly projecting. spring-likecontact fingers30', 32.- The moveable contact arm 28 is fixed to the shaft 20 by a head34 and moves directly with the shaft 20. Internally and externally ofthe turret 10, each of the contact fingers 16, 18 terminates in contactbuttons, suchas the pair indicated by the ref erence numerals 36, 38 and36 and 38' associatedwith the contact fingers 16, ISand-lfi and 18'. Thecontact, fingers and buttons are insulated: from the turret asshowninthe drawing.

In order to make contact withthe plate andcathode of the particulardiode to be arbitrarily designated as the standard S, there is provideda fixed-insulating support 40, carrying the fixed contact set 42, 44engageablewith thecontact buttons 36, 38 ofthe adjacent contact andsupporting fingers 16,- 18. Similarly, provision is made for electricalconnection to the spring-like contact fingers 30, 32 of themovablecontact arm 28, by supporting these: contactfingers on aninsulating head 46- and by extending leads 48, 50 to take-off rings 52,54' arranged externally of but electrically insulated from the shaft 20as shown. Contiguous to and in conductive contact with the take-offrings 52, 54 area contact set 56, sd-providing ready accessto the plateand cathode respectively of the particular diode T, designated asthediode under test.

A- suitable drive for the shaft 20 is provided by motor 60 coupled via areduction box 62 to the shaft proper. As is apparent, rotation of theshaft 20 moves the movable contact arm 28- through a complete comparisoncycleduring which the contact fingers 30', 32 engage successive pairs ofthecontact buttons 36, 38' of the diodes T to be compared to thearbitrarily designated standard S.

At the end of a comparison cycle' with one diode as an arbitrarystandard; mechanisms are provided for indexing the tu1ret'10 to bringthe next successive diode into electrical connection with the fixedcontact set 42, 44 to pro: vide plate andcathode contact respectivelywith afurther' diode to be arbitrarily designated as-a standard. Forthis purpose'a rotating disk 64 is fixed to the shaft 20 andprovidedwitha" switching arrangement 66-, adaptedto. close a control circuit in theposition: of the contact arm 28 corresponding to the endof a comparisoncycle. The con' trolcircuit includes a solenoid 68 connectable toapowerlineL, L, the solenoid GS-being arranged via a pawl 70 and aratchet- 72 to index the turret 10 at the end of a: comparison cycle.Other and varied mechanisms for co ordinating the indexing of the turret10 with-the beginning, of anew comparison cycle are apparent tothose-skilled in the art.

By means of this flexible arrangementthereare provided two pairs ofstationary contacts, one pair con nected to the cathode and plate of anarbitrary standard and the other pair connected successively to thecathodes and plates of diodes for comparison with the standard. Thesecontactsmay be incorporated into any of the known circuits forascertaining a particular diode characteristic.

For illustrative purposes a simple form of germanium diodeforward-characteristic balance comparator 74 has been illustrated forcomparing the successive arbitrary standards S with the remaining diodesT to be tested. The balance comparator 74 includes a pulse generator 76which is a source of periodically varying positive pulses as from analternating current full-wave rectifier. The output of the pulsegenerator is applied to terminals Sp and Tp which are connected tocontacts 42 and 56 respectively. The terminals Sk and Tk, connected tocontacts 44 and 58 respectively, are connected to ground through a pairof identical grid resistors 78 and 80 and also to the control grids of apair of tubes 82, 84 of identical characteristics. These tubes togetherwith the aforementioned grid resistors constitute essential elements ofa balance comparator which has its plates connected to a suitable sourceof plate potential and has its cathodes coupled together over cathoderesistors to ground. It is apparent that any number of stages ofintermediate amplification may be provided for plate or cathode couplingthe tubes 82, 84 of the balance comparator to a control relay coil 86,the operation of which is hereinafter explained.

In the operation of the apparatus, two situations can exist, namelysubstantial coincidence between the successive arbitrary standards S andthe diodes T under test, resulting in no current in the relay coilconnected across the common cathode circuit of the balance comparator,or a marked dilference in the characteristics of,

the diodes being compared resulting in current flow in the relay coilconnected across the common cathode circuit of the balance comparator.An interim condition existing when a test diode has been removed fromthe circuit and the next test diode has not made contact results in anunbalanced condition, and another interim condition existing when boththe test diode and the standard are being changed results in a balancedcondition of no current flow in the relay coil.

For the purposes of recording, a cylindrical drum 90 is fixed about theshaft 20 coaxially of the turret 10. Suitable means are provided on theturret 90 to secure a recording medium 92 thereon, the medium beingprovided with a column 92a and a row 92b for each of the diodessupported on the turret 10. Arranged longitudinally of therecordingmedium 92 and above the recording drum or cylinder 90 is a continuousbelt conveyor 94 carrying spaced printingmembers 96, the belt conveyorbeing supported on the rollers 98, 1.00. Arranged within the beltconveyor 94 for the printing members 96, is a stamping pad 102 backingup the lowermost run of the belt conveyor, the stamp pad 102 beingsupported by guide rods 104 received within fixed guide sleeves 106.Circumposed about the respective guide rods 104 are coil springs 108normally biasing the stamping pad 102 downwardly and causing theprinting member 96 to print along the column and row of the recordingmedium immediately therebeneath. The belt conveyor 94 of the printingmechanism is coordinated to the movable contact arm 28 through itsmovement through successive comparison cycles by means of a sprocket andchain drive 110 coupled via bevel gears 112, 114 to the shaft 20. Byappropriately spacing the printing members 96, it is possible to haveone printing member move along a column 92a, corresponding to theparticular diode arbitrarily designated as the standard S throughout agiven comparison cycle. Since the printing member is coordinated withthe movement of the contact arm, it will successively be in positionsopposite rows 92b corresponding to the diode T being instantaneouslycompared with the standard S. At the end of the given comparison cycle,a new column is brought into the printing position beneath the lower runof the printing belt, the next successive'printing member being inposition for movement along this column. Therefore, in order to deriveactual markings or indications on the recording medium 92 for thepurposes of sorting the respective diodes, it is necessary toelectrically operate the stamping pad or member 102 when substantialcoincidence exists between the devices under test and the arbitrarilydesignated standard. For this purpose, there is provided a relay arm 116connected to a suitable source of positive potential M and arranged foroperation under control of the relay coil 86. The relay arm 116 isbiased out of contact with a circuit-closing terminal 120 by a spring122, the terminal 120 completing the circuit from terminal M to terminalM through solenoid 124 upon fiow of current in relay coil 86. Solenoid124 is arranged to maintain the stamping pad member 102 in itsinoperative position against the oppositely-directed force exerted bythe springs 108 as long as terminal 120 and relay arm 116 are incontact. Since only the balanced condition results in de-energization ofthe relay coil 86, opening of the circuit for the solenoid 124, andrelease of the stamping member 102, the latter will normally bemaintained in its retracted or inoperative position by solenoid 124,thereby making no indications or record on the chart 92. It will ofcourse be obvious to those skilled in the art that by reversal of theoperation of the solenoid 124 and associated actuating springs 108, andthe operation of the switch comprising switch arm 116 and contact 120, acontrol signal can be transmitted from the comparison circuit to thesolenoid 124 upon coincidence of characteristics of a standard and atest device. In this way an impression would be made on the recordingmedium by the magnetic influence of the control signal rather than bythe mechanical force of a spring arrangement.

A typical comparison cycle during successive matching and testing of thediodes on the turret 10, each with every other diode, is substantiallyas follows:

The motor 60 is energized to cause the shaft 20 to rotate through acomparison cycle during which successive ones of the diodes T areelectrically connected in the comparison circuit 74 via the contact set56, 58, the arbitrarily designated standard being likewise connectedinto the comparison circuit 74 by the contact set 42, 44. If, forexample, the fifth diode tested has a substantially similarcharacteristic with reference to the standard, the printing member 96,which at that moment will be 0pposite the fifth row of the recordingmedium 92 and along the column corresponding to the particular diodearbitrarily designated as the standard, will be urged downwardly sincethe solenoid circuit124, will be opened by deenergization of the relaycoil 86. Therefore a mark will be recorded on the medium 92 indicatingthat the fifth diode corresponds to the standard with respect to thecharacteristic under consideration. The operation continues, and ifduring the cycle further diodes compare favorably with the standardappropriate indications will be recorded. At the end of the comparisoncycle, the switch arrangement 66 coordinated to the shaft 20 willcomplete the circuit for the indexing solenoid 68. Thereupon the pawland ratchet 70, 72 will index the turret 10 through an arc correspondingto the annular displace-- ment of the respective support and contactfingers 16, 18 to bring the next diode into connection with the contactset 42, 44 to arbitrarily serve as the standard. During this indexingstep no standard or test diodes will be connected in the comparatorcircuit, possibly for sufiicient time so that a mark will be recorded onthe medium 92. However, from the position of such a mark it will beobvious that it can be neglected in the analysis of the information onthe chart. The cyclic operation will com tinue with each successivediode serving as standard and being compared to every other diode on theturret. It

is to be noted that duplicate indications and recordings,

will be obtained when comparing the diodes, that is to say, if the firstdiode compares to the fifth diode when the first is designated as thestandard, then when the fifth is designated as the standard anotherindication will be obtained that the fifth diode is similar to thefirst: diode. By this duplication, it is possible to derive a checkgees, r56

5. (in the accuracy of the test system without the necessity ofrepeating the test; or by the provision of complex mechanisms.

From the foregoing, it can be seen that the present inveution' providesa method for grouping diodesidentical with respect to a givencharacteristic which-essentially comprises the steps of selecting one ofthe diodes as the standard and then matching the standard with each ofthe remaining diodes for the purposes of obtaining iiidic'ations whenthe given characteristic of the respective ones or the remaining diodessubstantially coincidewith the standard; These indications are recordedand; su i tably earmarked on a recording medium from which the matchedpairs or groups of four can be sorted: for use in a wide variety ofcircuits. I

An extension of the invention suggested from the matching of diodes oneagainst the other within a group, would be matching the group of diodesagainst one or more external standards, each of the group beingsequentially compared with the standards for the purposes or obtainingindications of coincidence in the character'- istic under consideration.

What I claim is:

l. A testing apparatus for matching groups of electrical devices havinga substantially similar characteristic comprising a carrier adapted tosupport a plurality of electrical devices, first contact means adaptedto be conductively connected to one of said electrical devicesarbitrarily designated as a standard, second contact means adapted to besuccessively connected to further ones of said electrical devices to betested, a measuring circuit conductively connected to said first andsecond contact means and arranged to compare the characteristic of saidstandard and the devices being tested, means responsive to saidcomparison circuit for recording coincidence in the characteristic ofsaid standard and the device being tested, and means for connecting tosaid first contact means a further one of said electrical devices to bedesignated as a standard in place of said one device.

2. A testing apparatus for matching groups of rectifying devices havinga substantially similar characteristic comprising a movable carrierincluding respective pairs of conductive fingers each adapted to engagethe terminals of a rectifying device, fixed test contacts adapted to beconductively connected to a selected one of said devices arbitrarilydesignated as a standard, movable comparison contacts adapted to besuccessively connected to further ones of said devices, a measuringcircuit including an input from said test and comparison contacts andarranged to provide an output when substantial coincidence existsbetween the characteristic of said standard and successive devicespaired therewith, means responsive to the output of said comparisoncircuit for recording coincidence in the characteristic of said standardand the paired device and carrier moving means for disconnecting saidselected one device from the fixed test contacts and for conductivelyconnecting a further one of said devices to the fixed test contacts.

3. A testing apparatus for matching groups of electrical devices havinga substantially similar characteristic comprising a rotatable carrieradapted to support a plurality of electrical devices, first contactsadapted to be conductively connected to a first one of said electricaldevices during a comparison cycle, second contacts movable relative tosaid carrier and adapted to be successively connected to further ones ofsaid electrical devices during the said comparison cycle, a measuringcircuit electrically connected to the respective contacts and arrangedto compare by pairs the characteristic of said first one of said devicesand successive ones of said devices, means responsive to said comparisoncircuit for recording coincidence in the characteristic of successivepairs under test, means for moving said second contacts through acomparison cycle, and carrier rotating means for disconnecting saidfirst one of said devices from lsaid first contacts and for conductivelyconnecting a second one of said devices to said first contacts.

4. A testing apparatus for matching groups of rectif ying devices of asimilar current-voltage characteristic adapted to' engage the terminalsof a rectifying device,

fixed test contacts adapted to be conductively connected to a selectedone of said rectifying devices during a 5 comparison cycle, movablecomparison contacts rotatable during said comparisoncycle to besuocessively connected to further ones of said rectifying devices, a-

balanced measuring circuit including aninput from said test andcomparison contacts and an output arrangedto provide a control voltagevvhensubstantial coincidence exists between the characteristic of saidone rectifying device and a paired further one of said rectifyingdevices, means responsive to the output of said comparison circuits forrecording coincidence in the characteristic of said successive paireddevices, means for rotating said comparison contacts through acomparison cycle, and means operable in dependence upon said last namedmeans for advancing said movable turret at the end of a comparison cycleto bring a further one of said rectifying devices into engagement withsaid fixed contacts.

5. A testing device for grouping diodes having a similar characteristiccomprising an intermittently indexable turret, a plurality ofperipherally spaced pairs of support and contact fingers on said turreteach adapted to engage the terminals of a diode, a fixed contact setengaging one of said pairs supporting a diode selected as a standard, amovable contact set adapted to engage successive ones of said pairs offingers supporting diodes to be compared to said standard, a recordingcylinder arranged concentrically of said turret and operativelyconnected thereto, said cylinder being arranged to support a recordingmedium having a column and row for each diode on said turret, a markingmember movable longitudinally of said cylinder in timed relation withsaid movable con tact set and along a path coinciding with and spacedfrom a column corresponding to the standard, a comparison circuitincluding an input from said fixed and movable contact sets and arrangedto provide a distinctive control in response to coincidence in thecharacteristic of said standard and the diode under test, and meansoperable by said distinctive control for urging said marking member intoa recording position relative to said cylinder whereby said markingmember provides an indication on said recording medium in the columncorresponding to said standard and in the row corresponding to thematched diode.

6. A testing device for grouping diodes having a similar characteristiccomprising an intermittently indexable turret including supports eachadapted to engage the terminals of a diode, a fixed contact set adaptedto conductively engage one of said diodes selected as a standard, amovable contact set adapted to conductively engage successive ones ofsaid diodes to be compared to said standard, a recording cylinderarranged concentrically of said turret and operatively connectedthereto, said cylinder being arranged to support a recording mediumhaving a column and row for each diode on said turret, printing meansmovable along successive columns of said recording medium in timedrelation with said movable contact set, a comparison circuit includingan input from said fixed and movable contact sets and arranged toprovide a distinctive control in response to coincidence in thecharacteristic of said standard and the diode under test, and meansoperable in dependence upon said distinctive control for moving saidprinting means intoa recording position relative to said cylinder.

7. A testing device for grouping diodes having a similar characteristiccomprising an intermittently indexable turret adapted to support aplurality of diodes, operating means for indexing said turret at the endof a comparison cycle, a fixed contact set adapted to engage individualdiodes selected as standards during successive comparison cycles, amovable contact set adapted to engage the remaining diodes during agiven comparison cycle to be compared to the one diode selected as astandard, a recording cylinder arranged concentrically of said turretand operatively connected thereto, said cylinder being arranged tosupport a recording medium having a column and row for each diode onsaid turret, a printing member adapted to be moved longitudinally ofsaid cylinder in timed relation with said movable contact set and alonga path coinciding with and spaced from a column corresponding to the onediode selected as a standard, operating means for moving said movablecontact set and timed printing member through a comparison cycle wherebysaid printing member is successively arranged along rows of saidrecording medium corresponding to the diodes under test, a comparisoncircuit including an input from said fixed and movable contact sets andarranged to provide a distinctive control in response to a coincidencein the characteristic of standard and the diode under test, and meansoperable by said distinctive control for displacing said printing memberinto a recording position relative to said cylinder References Cited inthe file of this patent UNITED STATES PATENTS Flahertz May 29,

